Method for explosively bonding metal layers



July 5, 1966 A. A. POPOFF 3,

METHOD FOR EXPLOSIVELY BONDING METAL LAYERS Filed Jan. 25, 1963 2Sheets-Sheet 1 INVENTOR ALE XIS A. POPOFF BY July 5, 1966 A. A. POPOFFMETHOD FOR EXPLOSIVELY BONDING METAL LAYERS Filed Jan. 23, 1963 2Shets-Sheet 2 IN VENTOR United States Patent 3,258,841 METHUD FOREXPLOSIVELY BONDING METAL LAYERS Alexis A. Popoif, Woodbury, N.J.,assignor to E. I. du

Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware Filed Jan. 23, 1063, Ser. No. 253,485 6 Claims.(Cl. 29-486) The present invention relates to an improved method ofbonding metals by explosive means.

A process has been described recently for bonding metal layers to form amultilayered body by supporting a metal cladding layer a distance of atleast 0.001 inch from a metal base layer, placing a layer of anexplosive having a detonation velocity less than 120% of the sonicvelocity of the metal having the highest sonic velocity in the system onthe outside surface of the metal cladding layer, and initiating theexplosive so that detonation is propagated parallel to the metal layers.Although the bonding obtained by this process is excellent, some areasaround the edges of the composite systems may be left unbonded. Thisproblem is particularly acute when the metal layers and the explosivelayer are substantially rectangular and the explosive layer is initiatedby means of a blasting cap, detonating cord, or some other devicepositioned at a point or points along one edge of the layer. In themajority of cases the largest unbonded zone extends over an essentiallyrectangular area along that edge of the composite system which wascontiguous to the point or points of initiation.

This ditficulty is overcome and a completely bonded clad metal system isproduced by 1) Providing metal extension pieces on at least one of theedges of a metal cladding layer, each of said metal extension piecesbeing contiguous to an edge of the metal cladding layer forsubstantially the length of said edge, extending in a directionperpendicular to said length of the edge of the cladding layer adistance at least four times the thickness of the metal cladding layer,and having an areal density of at least 50% and no more than 150% of theareal density of said metal cladding layer,

(2) Supporting said metal cladding layer substantially parallel to andseparated by a distance of at least 0.01 inch from a metal base layer,

(3) Covering the area defined by the outside surfaces of said metalcladding layer and extension pieces with a layer of a detonatingexplosive having a detonation velocity between about 1200 meters persecond and 120% of the sonic velocity of the metal having the highestsonic velocity in the system, and

(4) Initiating the explosive layer so that detonation is propagatedparallel to the plane of the metal cladding layer and the metalextension pieces are sheared from the metal cladding layer.

For a more complete understanding of the process of the presentinvention reference is now made to the attached drawings in which likenumbers indicate similar elements and in which FIGURES 1-7 representcross-sectional views of assemblies which may be used for the practiceof the present invention, and

FIGURES 8 12 represent top views of portions of assemblies which may beused for the practice of the present invention.

In FIGURES 1-7 metal cladding layer 1 to which are attached metalextension pieces 2 is positioned above metal base layer 3 (supportingmeans are not shown). The upper surfaces of metal cladding layer 1 andmetal extension pieces 2 are covered with a layer of a detonatingexplosive 4 to which is attached an electric blasting cap ice 5 havinglead wires 6 to a source of electric current. In FIGURE 4 the jointsbetween metal cladding layer 1 and metal extension pieces 2 are coveredwith metai strips 7 which serve as gas blockers preventing detonationgases from flowing through these joints and entering the space betweenmetal layers 1 and 3.

FIGURES 8-12 depict the upper surfaces of the metal extension pieces 2.and of the metal cladding layer 1 to which the metal extension pieces 2are attached. The term metal cladding layer in this application refersto that layer which is explosively bonded to the metal base layer by theprocess of the present invention. In FIG- URES 8-12 the upper surface ofeach metal cladding layer 1 is defined by the area ABCD and the hatohedlAlternatively, the metal extension pieces 2 can be provided in the formof a metal picture frame as shown in FIGURES 7 and 12. In FIGURE 12, thebroken lines, AB, BC, CD, and DA, correspond to the edges of metalcladding layer 1 which are overlapped by the edges of the extensionpieces 2. Obviously, metal extension pieces 2 can be attached to one,two, three, or four edges of metal cladding layer 11 and can compriseintegral parts of a single metal plate or layer or separate pieces ofmetal attached to edges of metal cladding layer 1 by any of severalmethods which will be more fully described hereinafter.

The term metal in this application includes any ele- The composition,loading, and confinement of the explosive layer, and the particulardevice(s) used to initiate the explosive layer must be selected so thatthe detonation velocity of the explosive remains within the limits givenabove and so that detonation is propagated parallel to the metalcladding layer.

The minimum separation or standoif between the metal layers whichresults in a strong, continuous metal-to-metal bond is about 0.01 inch.The optimum size of this standoff depends upon a number of factorsincluding the metal cladding layer thickness and density and theexplosive loading, confinement, and detonation velocity. The specificspacing members used to provide this standoff must not be such as tointroduce .a large mass of foreign material or cause entrapment of airin the bond zone between the metal layers.

Although there is no intention to be limited by any theory of operationit is believed that unbonded zones around the edges of an explosivelyclad metal system are attributable, at least in part, to a lag in thevelocity of the edge-s of the metal cladding layer as compared with thevelocity of the center of the layer when the metal cladding layer ispropelled by the pressure exerted by a uniform layer of explosive. Thislag in velocity is caused by the boundary conditions which exist alongthe free surfaces, i.e., at the edges of the explosive layer. Since thefree surfaces must remain at atmospheric pressure, when the explosive isinitiated, rarefaction waves are formed at the edges of the explosivelayer. Lower pressure is a exerted on the edges of the metal claddinglayer than is exerted on the center of the layer and lower velocity isimparted to the edges than is imparted to the center of the layer. Thus,each edge strikes the corresponding edge of the base layer withinsufiicient velocity to produce the plastic deformation required toestablish a bond.

When the explosive is initiated at a point or points along one edge ofthe layer, the problem of unbonded zones is particularly acute alongthat edge of the clad metal system which corresponds to the initiationedge of the layer of explosive. Although the cause of this uniquedifliculty is not fully understood, it is probable that a number offactors are involved.

Explosive bonding within the sense and scope of this invention generallyis accompanied by a jetting phenomenon. When the metal cladding and baselayers collide at an angle which is critical for a given value of thesonic velocity of the metal layers and the detonation velocity .of theexplosive layer, a jet composed of molten surface portions of both metallayers is formed, circulated, and solidified between the layers.However, when the explosive is initiated at a point or points along eneedge of the layer, for a very small distance, this edge of the metalcladding layer may be propelled essentially normal to the metal baselayer and thus fail to form the critical angle necessary for jetting.The eifects of this geometrical consideration, the edge lag describedabove, and the anomalies associated with start-up of detonation of theexplosive layer combine to intensify the problem of unbonded zones alongthe initiation edge. When the explosive is initiated at one corner ofthe layer this combination of factors is detrimental to bonding alongthe two edges adjacent to the initiation corner and when one entire edgeof the layer is initiated simultaneously, for example, by means of aline wave generator the geometry and dynamics of the system often leadto large unbonded zones along all of the edges except that edge directlyopposite to the initiation edge. Furthermore, even in cases in whichjetting occurs over the entire interface between the metal layersdetonation gases often enter the space between the two layers andprevent formation of a good metal-to-metal bond around the periphery ofthe system.

The average width of the unbonded zones along the edges of the claddinglayer increases with the thickness of the cladding layer. For example,when the cladding layer is inch thick unbonded zones at least A inchwide are observed and when the cladding layer is more than inch thickthere is at least a proportional increase in the width of the unbondedzones, i.e., the width of the unbonded zones generally is at least about4 times the thickness of the cladding layer. However, if extensionpieces inch thick and inch wide A inch wide not counting the overlapwhen using extension pieces as shown in FIGURE 12) are attached to oneor more of the edges of the A -inch thick cladding layer, i.e., so thateach extension piece extends 4 inch normal to the length of the edge towhich it is attached, the lagging edges and their attendant difiicultiesare efiectively removed from the area to be bonded. The width of a metalextension piece normal to the edge to which it is attached, e.g., thewidth DF or CE in FIGURE 7 or 12, must be at least 4 times the thicknessof the metal cladding layer in order to insure complete bonding alongthe edge to which it is attached, i.e., the edge DC in FIGURE 7. Whenthe cladding layer is very thin, for example, on the order of a few milsthick, the extension pieces are generally considerably wider than fourtimes the thickness of the cladding layer simply because of thedifliculty of working with narrow strips of thin metal sheets. Howeverfor obvious economic reasons, the width of the extension pieces shouldbe kept as close to the minimum as possible.

The number of extension pieces which must be used to insure anessentially completely bonded clad metal system depends, among otherthings, upon the thickness and shape 'of the cladding layer and upon thelocation of the p0int(s) of initiation of the explosive layer. When thecladding layer is relatively thin the unbonded zones attributed simplyto edge lag are relatively narrow and the cost of trimming the unbondededges may be comparable to or less than the cost of providing extensionpieces on all four edges of the cladding layer. However, in such cases,as explained above the unbonded zones along the edge or edges of theclad metal system which are contiguous to the point or points ofinitiation of the layer of explosive are considerably wider than thosealong the other edges of the system. Thus, referring to FIG- URE 7, forexample, if the layer of explosive is to be initiated at a point alongthat edge of the layer which cor responds to edge DC of the metalcladding layer a single metal extension piece attached as shown inFIGURE 7 is sufficient to eliminate unbonded zones of any significantwidth. Obviously the layer of explosive covers the surface of theextension piece as well as that of the metal cladding layer and isinitiated at a point along the line FE. Other practical arrangements forcladding with a relatively thin metal cladding layer include thoseillustrated in FIGURES 9 and 10. In the former case the explosive isinitiated at that corner of the layer of explosive which is contiguousto the juncture between the extension pieces, as in Example 5. Thearrangement shown in FIGURE 10 can be used in conjunction with alinewave generator which initiates the explosive along the edge oppositeto that edge of the cladding layer to which no extension piece isattached as in Example 7. When the cladding layer is relatively thick,four extension pieces are generally necessary to insure a completelybonded clad metal system. As mentioned above, each extension piece is atleast four times as wide as the thickness of the cladding layer. Whenthe explosive is initiated at a point or points along one edge of theexplosive layer it is desirable to use a metal extension piece of morethan the minimum width along the contiguous edge of the cladding layer.This provides additional protection to counteract the problemsassociated with the initiation edge. If center initiation is used thisprecaution is unnecessary.

Ideally the layer of explosive detonates parallel to the plane of themetal cladding layer and accelerates the extension pieces and thecladding layer with essentially uniform velocity. When the jont betweenan extension piece and an edge of the metal cladding layer is continuousand the areal densities of the extension piece and cladding layer arecomparable, e.g., as shown in FIG- URE 1, there is essentially novelocity differential across the joint. However, we have found that theareal density of an extension piece can vary between about 50 and 150percent of the areal density of the cladding layer and still beeffective in essentially eliminating unbonded zones along the edge towhich it is attached. When the areal density of the extension piece isoutside these limits the velocity differential between the extensionpiece and the cladding layer which is due to the edge-lag effectdescribed above is insignificant compared to the velocity differentialacross the joint which is due to the widely differing areal densities ofthe extension piece and cladding layer. If the areal density of theextension piece is less than 50 percent of that of the cladding layerthe extension piece is accelerated to a higher velocity than is thecladding. layer and the joint between the extension piece and thecladding layer is put under such strain that it often breaks before thebond between the edges of the cladding and base layers is establishedthus permitting, for example, entry of detonation gases into the spacebetween the layers and preventing formation of a good metallurgical bondbetween the two layers. It the areal density of the extension piece ismore than 150 percent of that of the cladding layer, the cladding layeris accelerated to a higher velocity than is the extension piece andagain the joint between the cladding layer and extension piece isstrained with the deleterious effects described above.

Obviously, the strength of this joint will vary depending upon, forexample, whether the cladding layer and extension piece are sections ofa single plate or separate pieces of metal joined by welding, epoxyresin, etc. Often it is sufiicient to simply lay the picture frame shownin FIGURE 12 on top of the cladding layer. Detonation of the explosivelayer effectively shears and removes the extended portions of thepicture frame from the clad metal system and the overlapped portions ofthe picture frame either are shattered and blasted away from the systemduring detonation or are easily removed after detonation.

For most systems the above-defined limits with respect to areal densityrepresent practical limits within which the process of the presentinvention can satisfactorily be carried out. These limits can besatisfied in a number of ways. First, the extension pieces can be of thesame thickness and composition as the metal cladding layer. Oneconvenient method of practicing the present invention comprises using ametal cladding layer which is oversize with respect to the base layer onone or more edges as described above in connection with FIGURE 7 anddescribed hereinafter in Examples 1, 3 and 6. If, however, the claddinglayer is so thick that the extending edges are not sheared during theexplosive process, the extension pieces can be prepared from metalplates of the same thickness and composition as the cladding layer andcan be attached to the cladding layer by a bond which does break or giveduring the cladding process.

Since the cladding layer often comprises an expensive metal which isbonded to the base layer to give the composite some specific desirableproperty such as high corrosion resistance, the cost of extension piecesof the same metal as the cladding layer is often prohibitive. In suchcases the extension pieces can be of the same thickness as the claddinglayer but made of a different metal having a density comparable to thatof the cladding layer as in FIGURE 1.

Extension pieces of substantially higher or lower density (weight perunit volume) than the cladding layer are also satisfactory. In order tocompensate for the difference in density the thickness of the extensionpieces is adjusted so that the weights per unit area or areal densitiesof the extension pieces and the cladding layer are within the limitsdefined above. FIGURES 2, 5, and 6 illustrate assemblies wherein theextension pieces are thicker than the cladding layers. The inner cornersof the extension pieces can be square as in FIGURES 2 and 5 or obtuseangles as in FIGURE 6. FIGURE 3 illustrates an assembly in which theextension pieces are thinner than the cladding layer.

The joints between the cladding layer and the extension pieces must bestrong enough to support the Weight of the explosive layer and anyconfining medium which is used and weak enough to allow the extensionpieces to be completely sheared from the cladding layer during theexplosive operation. If the bonds between the cladding layer andextension pieces are too strong or if obstructions which offersufiicient resistance to the motion of the extension pieces are placedbelow the extension pieces, the extension pieces spring back or spall orpartially shear and pull the cladding and base layers apart thuspreventing bonding and/or allowing entry of detonation gases into thespace between the two layers. Suitable methods of attachment are, forexample, cement, epoxy resin, and shallow, metallic welds.

If the edges of the cladding layer are rough or uneven it is difficultto provide extension pieces flush with the edges of the layer. In suchcases it is advisable to fill the gaps with a material such as ametal-filled epoxy resin or solder which serves as a method of attachingthe extension pieces to the cladding layer and has a density in therange of that of the metal extension pieces and cladding layer. Theentry of detonation gases into the space between the metal layers isseriously detrimental to the formation of a good bond. The detonationgases can, for example cushion" and thus reduce the velocity of thecladding layer and/or react with the metal of the cladding or base layerto form a deleterious oxide phase. Filling the gaps between the edges ofthe cladding layer and extension pieces can prevent the detonation gasesfrom flowing through the joints and between the metal layers. However,use of metal strips as gas blockers arranged over the joints as inFIGURE 4 or of the assembly shown in FIGURES 7 and 12 is a necessaryprecaution in many cases.

The configuration of the joints between the extension pieces and thecladding layer is not critical provided that the extension pieces shearfrom the cladding layer and detonation gases are prevented from enteringthe bonding zone. A simple butt joint as illustrated in FIGURES 1 to 6is a particularly convenient configuration. However any practicablebeveled or notched joint is satisfactory. The extension pieces can berectangular as illustrated in FIGURES 8 to 11 or trapezoidal asillustrated in FIGURE 12 in which case a joint between any two extensionpieces will form obtuse angles with the joints between the extensionpieces and the corresponding edges of the cladding layer.

The following examples illustrate some of the modifications of theprocess of the present invention. They are intended as illustrativeonly, however, and are not to be considered as exhaustive or limiting.

Example 1 A stainless steel plate inch thick, 6 inches wide, and 10inches long is positioned above and parallel to a mild steel plate /2inch thick, 6 inches wide, and 9 inches long so that a 1-inch segment ofthe length of the stainless steel plate extends beyond the mild steelplate substantially as illustrated in FIGURE 1. -T he adjacent surfacesof the two plates are separated by a distance of .060 inch maintained byshim steel cups .060 inch deep and inch in diameter, one of which isspot welded in each of the four corners of the upper surface of the mildsteel plate. The upper surface of the stainless steel plate is coveredwith a sheet of a fibrous explosive composition comprising 75 partspentaerythrito-l tetranitrate, 17.5 parts of a butadiene-acrylonitrilerubber, and 7.5 parts paper pulp and having a weight distribution of 4grams per square inch. This explosive detonates at a velocity of about3600 meters per second. An electric blasting cap havinrg lead wires to asource of electric current is attached to the center :of that edge ofthe layer of explosive which is contiguous to the extended edge of thestainless steel plate. The entire assembly is covered with a pile ofsand 1 foot deep. A piece of cardboard glued to the extended edge of thestainless steel plate perpendicular to the plate keeps the spacedirectly beneath the stainless steel extension free of sand. Theblasting cap which is actuated by application of electric currentinitiates the layer of explosive. During detonation, the stainless steelextension is sheared from the plate and a stainless steel-onmild steelcomposite 6 inches wide and 9 inches long is formed. Ultrasonic probingreveals no unbonded zones around the edges of the metallungically bondedclad metal system.

Example 2 A clad metal system of the composition, dimensions, andquality described in Example 1 is prepared using the materials and amodification of the technique described in Example 1. In this examplethe stainless steel plate is inch thick, 6 inches wide, and 9 incheslong. A piece of mild steel inch thick, 1 inch wide and 6 inches long isbutted along its length against one of the 6-inch edges of the stainlesssteel plate and glued in place with epoxy resin thus forming a mildsteel extension to the stainless steel plate substantially asillustrated in FIG- URE 1. During detonation, the mild steel extensionis sheared from the stainless steel plate and a stainless steelon-mildsteel composite 6 inches wide and 9 inches long is formed. Again,ultrasonic probing reveals no unbonded zones around the edges of themetallurgically bonded composite.

Example 3 A stainless steel plate inch thick, 7 inches wide and. 10 /2inches long is positioned above and parallel to a mild steel plate /2inch thick, 6 inches wide and 9 inches long so that one of the 7-in'chedges of the stainless steel plate extends 1 inch beyond the adjacent6-inch edge of the mild steel plate and each of the other 3 edges of thestainless steel plate extends /2 inch beyond the corresponding adjacentedge of the mild steel plate. The adjacent surface of the two plates areseparated by a distance of .060 inch maintained as in Example 1. Theupper surface of the stainless steel plate is covered with a layer of aIgrained amatol explosive comprising 50 parts ammonium nitrate and 50parts itrinitrotoluene. The layer of explosive, which is contained by arectangular wooden frame about 4; inch thick and 1 inch high placed onthe perimeter of the upper surface of the stainless steel plate, isin-ch thick and has a detonation velocity of about 3500 meters persecond. An electric blasting cap is attached to the wooden frame in thecenter of that edge of the layer of explosive which is contiguous to theedge of the stainless steel plate which extends 1 inch beyond the mildsteel plate. The layer of explosive is covered; with a sheet of waxedpaper and the entire assembly iscovered with a pile of sand 5 feet deep.Pieces of cardboard glued around the edges of the stainless steel plateperpendicular to the plate keep the space directly beneath theextensions free of sand. The blasting cap is actuatedv by application ofelectric current and initiates the layer of explosive. During detonationthe stainless steel extensions are sheared from the plate and astainless steel-onmild steel composite 6 inches wide and 9 inches longis formed. Ultrasonic probing reveals no unbonded zones around the edgesof the metallurgically bonded clad metal system.

Example 4 A clad metal system of the composition, dimensions and qualitydescribed in Example 3 is prepared using the materials and amodification of the technique described in Example 3. In this examplethe stainless steel plate is A; inch thick, 6 inches wide, and 9' incheslong. A piece of mild steel /8 inch thick, 1 inch wide, and 6 /2 incheslong is butted along its length against one of the 6-inch edges of thestainless steel plate so that a [2-inch segment of the length of themild steel extends beyond the end of the 6-inch edge of the stainlesssteel plate. A second piece of mild steel inch thick, /2 inch wide and 9/2 inches long is butted along its length against one of the 9-inchedges of the stainless steel plate so that one of the ends is flush withthe 90 angle formed by the extension of the first piece of mild steeland the 9-inch edge of the stainless steel plate and the other e-ndextends /2 inch beyond the 9-inch edge of the stainless steel plate. Athird piece of mild steel A; inch thick, /2 inch wide, and 6 /2 incheslong is butted along its length against the second 6-inch edge of thestainless steel plate so that one of the ends is flush with the 90 angleformed by the extension of the second piece of mild steel and the second6-inch edge of the stainless steel plate and the other end extends /2inch beyond the second 6-inch edge of the stainless steel plate. Afourth piece of mild steel inch thick, /2 inch wide and 10 inches longis butted along its length against the remaining 9-inch edge of thestainless steel plate so that one of the ends is flush with the 90 angleformed by the third piece of mild steel and the 9-inch edge of thestainless steel plate and the other end extends 1 inch beyond the end ofthe 9-inch edge of the stainless steel plate and is flush with the1-inch edge of the first piece of mild steel. The four pieces of mildsteel are glued in place with epoxy resin thus forming a 1-inchextension on one end of the stainless steel plate 8 and /2 inchextensions on the remaining 3 sides of the plate substantially asillustrated in FIGURE 9.

The cladding process is carried out as in Example 3. During detonationall four mild steel extensions are sheared from the stainless steelplate and a stainless steelon-mil-d steel composite 6 inches wide and 9inches long is formed. Ultrasonic probing reveals no unbonded Zonesaround the edges of the metallurgically bonded clad metal system.

Example 5 A nickel plate A; inch thick, 18 inches wide, and 18 incheslong is positioned above and parallel to a mild steel plate /2 inchthick, 18 inches wide and 18 inches long. The adjacent surfaces of thetwo plates are separated by a distance of .060 inch maintained as inExample 1. A piece of mild steel inch thick, 1 inch wide and 18 incheslong is butted along its length against one of the 18-inch edges of thenickel plate. A second piece of mild steel A3 inch thick, 1 inch wideand 19 inches long is butted along its length against an adjacent18-inch edge of the nickel plate so that one end extends 1 inch beyondthe end of the 18-inch edge of the nickel plate and is flush with the 1inch edge of the first piece of mild steel. The two pieces of mild steelare glued in place with epoxy resin thus forming l-inch extensions on 2adjacent edges of the nickel plate. The upper surfaces of the nickelplate and the mild steel extensions are covered with a %-inch layer ofthe explosive described in Example 3, contained in a wooden frame as inExample 3. An electric blasting cap is attached to the wooden frame inthat corner of the layer of explosive which is contiguous to the cornerat which the mild steel extension pieces meet. The layer of explosive iscovered with a sheet of waxed paper and the entire assembly is coveredwith a pile of sand 5 feed deep. Pieces of cardboard glued to the edgesof the mil-d steel extension pieces as in the preceding examples keepthe space directly beneath the extension pieces free of sand. Theblasting cap is actuated by application of electric current andinitiates the layer of explosive. During detonation the two mild steelextension pieces are sheared from the nickel plate and a nickel-on-mildsteel composite 18 inches wide and 18 inches long is formed. Ultrasonicprobing reveals no unbonded zones along the edges of the metallurgicallybonded clad metal system.

Example 6 A copper plate /8 inch thick, 7 inches wide, and 13 incheslong is positioned above and parallel to a mild steel plate /2 inchthick, 6 inches wide, and 12 inches long so that one of the 7-inch edgesof the copper plate extends 1 inch beyond the adjacent 6-inch edge ofthe mild steel plate and each of the 13-inch edges of the copper plateextends /2 inch beyond the corresponding, adjacent 12-inch edge of themild steel plate. The adjacent surfaces of the two plates are separatedby a distance of .060 inch maintained as in Example 1. The upper surfaceof the copper plate is covered with a 4-inch layer of the explosivedescribed in Example 3, contained in a wooden frame as in Example 3. Anelectric blasting cap is attached to the wooden frame in the center ofthat edge of the layer of explosive which is contiguous to the edge ofthe copper plate which extends 1 inch beyond the mild steel plate. Thelayer of explosive is covered with a sheet of waxed paper and the entireassembly is covered with a pile of sand 5 feet deep. Pieces of cardboardglued to the three extended edges of the copper plate as in thepreceding examples keep the space directly beneath the extensions freeof sand. The blasting cap is actuated by application of electric currentand initiates the layer of explosive. During detonation the copperextensions are sheared from the plate and a copper-on-mild steelcomposite 6 inches wide and 12 inches long is formed. Ul-

trasonic probing reveals no unbonded zones along the edges of themetallurgically bonded clad metal system.

Example 7 A clad metal system of the composition, dimensions and qualitydescribed in Example 6 is prepared using the materials and amodification of the technique described in Example 6. In this examplethe copper plate is A; inch thick, 6 inches wide, and 12 inches long. Apiece of mild steel inch thick, 1 inch wide and 6 /2 inches long isbutted along its length against one of the 6-inch edges of the copperplate so that a /z-inch segment of the length of the mild steel extendsbeyond the end of the 6-inch edge of the copper plate. A second piece ofmild steel inch thick, /2 inch wide, and 12 inches long is butted alongits length against one of the 12- inch edges of the copper plate so thatone of the ends is flush with the 90 angle formed by the extension ofthe first piece of mild steel and the 12-inch edge of the copper plate.A third piece of mild steel A; inch thick, /2 inch wide, and 13 incheslong is butted along its length against the second 12-inch edge of thecopper plate so that one end extends 1 inch beyond he end of the 12-inch e-dge of the copper plate and is flush with the 1-inch edge of thefirst piece of mild steel. The three pieces of mild steel are glued inplace with epoxy resin thus forming a l-inch extension on one end of thecopper plate and /z-inch extensions on the two long edges of the copperplate.

The cladding process is carried out substantially as in Example 3.However, in this example the layer of explosive is initiated by atriangular line-wave generator which is attached along that edge of thelayer of explosive which is contiguous to the edge of the 1-inch mildsteel extension. The line-wave generator is initiated by an electricblasting cap attached to the apex of the generator. During detonationthe three mild steel extensions are sheared from the copper plate and acopper-on-mild steel composite 6 inches Wide and 9 inches long isformed. Ultrasonic testing reveals no unbonded zones along the edges ofthe metallurgically bonded clad metal system.

Example 8 A tantalum plate .040 inch thick, 12 inches wide and 24 incheslong is positioned above and parallel to a mild steel plate inch thick,12 inches wide, and 24 inches long. The adjacent surfaces of the twoplates are separated by a distance of .045 inch maintained by two shimsteel ribbons one of which is spot welded along the length of the uppersurface of the mild steel plate, parallel to and 1 inch in from each ofthe 24-inch edges of the plate. Each of these ribbons is .001 inch thickand .045 inch wide, and is deformed normal to its thickness into a sinewave configuration of 3 cycles per linear inch and approximately .050inch amplitude. Each ribbon is placed on edge on the surface of theplate, i.e., so that the .045-inch dimension of the ribbon isperpendicular to the plane of the plate. Four mild steel extensionpieces are attached to the tantalum plate as described in Example 4.However, in this case each of the pieces of mild steel is .060 inchthick and 1 inch wide. The mild steel extension pieces attached to the12-inch edges of the tantalum plate are 13 inches long and thoseattached to the 24-inch edges of the plate are 25 inches long. Thepieces of mild steel are glued in place with epoxy resin thus formingl-inch extensions on each of the four edges of the tantalum platesubstantially as illustrated in cross-section in FIGURE 2. The uppersurfaces of the tantalum plate and the mild steel extension pieces arecovered with a layer of a grained soda amatol explosive comprising equalparts of ammonium nitrate, sodium nitrate, and trinitrotoluene. Thelayer of explosive which is contained in a wooden frame as in Example 3is .375 inch thick over the mild steel extension pieces and .395 inchthick over the tantalum plate. The average weight distribution of theexplosive is approximately 6 grams per square inch and the detonationvelocity is 3100 meters per second. An electric blasting cap is attachedto the wooden frame in the center of one of the edges of the layer ofexplosive which is contiguous to one of the 13-inch extension pieces andthe layer of explosive is covered with a sheet of waxed paper. Theentire assembly is covered with a wooden box which is in turn coveredwith a pile of sand. The blasting cap is actuated by application ofelectric current and initiates the layer of explosive. Duringdetonation, the four mild steel extension pieces are sheared from thetantalum plate and a tantalum-onmild steel composite 12 inches wide and24 inches long is formed. Ultrasonic probing reveals no unbonded zonesalong the edges of the metallurgically bonded clad metal system.

Example 9 A tantalum-on-mild steel composite of the dimensions describedin Example 8 is prepared using the materials and a modification of thetechnique described in Example 8. However in this example each of themild steel extension pieces is 1 /2 inches, rather than 1 inch wide, thetwo shorter pieces are 12 /2 inches long, and the two longer pieces are24 /2 inches long. The four pieces are welded together to form arectangular picture frame, the perimeter of which is 14 inches wide by26 inches long and each side of which is 1 /2 inches wide. Therectangular frame is laid on top of the cladin-g layer substantially asillustrated in FIGURE 12 so that a /2-inch segment of each side of theframe overlaps the cladding layer. The frame is spot-welded in place anddetonation is carried out substantially as in Example 8. However, inthis example the blasting cap is positioned in the center of the layerof explosive. During detonation the portions of the frame which extendbeyond the cladding layer are sheared from the assembly and theoverlapping portions of the frame are effectively blasted free of thesurface of the composite system. Ultrasonic probing reveals no unbondedzones along the edges of the metallurgically bonded clad metal system.

The invention having been fully described in the foregoin-g it is to belimited only by the following claims.

What is claimed is:

1. A process for producing a completely bonded clad metal system whichcomprises (1) providing metal extension pieces on at least one of theedges of a substantially rectangular metal cladding layer, each of saidmetal extension pieces being contiguous to an edge of the metalcladdin-g layer for substantially the length of said edge, extending ina direction perpendicular to said length of the edge of the claddinglayer a distance of at least four times the thickness of the metalcladding layer, and having a weight distribution per unit area of atleast 50% and no more than 150% of the weight distribution per unit areaof the metal cladding layer,

(2) supporting said metal cladding layer substantially parallel to andseparated by a distance of at least 0.01 inch from a substantiallyrectangular metal base layer,

(3) covering the area defined by the outside surfaces of said metalcladding layer and extension pieces with a layer of a detonatingexplosive having a detonation velocity between about 1200 meters persecond and of the sonic velocity of the metal having the highest sonicvelocity in the system and (4) initiating the explosive layer so thatdetonation is propagated parallel to the plane of the metal claddinglayer and the metal extension pieces are sheared from the metal claddinglayer.

2. A process as in claim 1 wherein a single metal extension piece isprovided on one of the edges of the metal cladding layer and theexplosive is initiated along that edge of the explosive layer which isparallel and adjacent 1 1 to that edge of the metal cladding layer towhich the extension piece is attached.

3. A process as in claim 1 wherein one metal extension piece is providedon each of the four edges of the metal cladding layer.

4. A process as in claim 3 wherein the explosive is initiatedsubstantially in the center of the layer of explosive.

5. A process as in claim 1 wherein metal extension pieces are providedon each of the two adjacent edges of the metal cladding layer and theexplosive is initiated at that corner of the layer of explosive which iscontiguous to the juncture between the metal extension pieces.

6. A process as in claim 1 wherein metal extension pieces are providedon three edges of the metal cladding layer and the explosive isinitiated along that edge of the layer of explosive which is opposite tothat edge of the metal cladding layer to which no extension piece isattached.

' References Cited by the Examiner UNITED STATES PATENTS 3,137,9376/1964 Cowan et a1. 29497.5 XR 3,197,855 8/1965 Carter et al 29470.1

JOHN F. CAMPBELL, Primary Examiner.

1. A PROCESS FOR PRODUCING A COMPLETELY BONDED CLAD METAL SYSTEM WHICH COMPRISES (1) PROVIDING METAL EXTENSION PIECES ON AT LEAST ONE OF THE EDGES OF A SUBSTANTIALLY RECTANGULAR METAL CLADDING LAYER, EACH OF SAID METAL EXTENSION PIECES BEING CONTIGUOUS TO AN EDGE OF THE METAL CLADDING LAYER FOR SUBSTANTIALLY THE LENGTH OF SAID EDGE, EXTENDING IN A DIRECTION PERPENDICULAR TO SAID LENGTH OF THE EDGE OF THE CLADDING LAYER A DISTANCE OF AT LEAST FOUR TIMES THE THICKNESS OF THE METAL CLADDING LAYER, AND HAVING A WEIGHT DISTRIBUTION PER UNIT AREA OF AT LEAST 50% AND NO MORE THAN 150% OF THE WEIGHT DISTRIBUTION PER UNIT AREA OF THE METAL CLADDING LAYER, (2) SUPPORTING SAID METAL CLADDING LAYER SUBSTANTIALLY PARALLEL TO AND SEPARATED BY A DISTANCE OF AT LEAST 0.01 INCH FROM A SUBSTANTIALLY RECTANGULAR METAL BASE LAYER, (3) COVERING THE AREA DEFINED BY THE OUTSIDE SURFACES OF SAID METAL CLADDING LAYER AND EXTENSION PIECES WITH A LAYER OF A DETONATING EXPLOSIVE HAVING A DETONATION VELOCITY BETWEEN ABOUT 1200 METERS PER SECOND AND 120% OF THE SONIC VELOCITY OF THE METAL HAVING THE HIGHEST SONIC VELOCITY IN THE SYSTEM AND (4) INITIATING THE EXPLOSIVE LAYER SO THAT DETONATION IS PROPAGATED PARALLEL TO THE PLANE OF THE METAL CLADDING LAYER AND THE METAL EXTENSION PIECES ARE SHEARED FROM THE METAL CLADDING LAYER. 